It is well-known to provide hand tools with a power source. Typically the power source used is electricity, either from batteries or from a mains outlet. However the prior art also discloses the use of alternative power sources for tools and other hand-held implements.
For example, U.S. Pat. No. 6,045,534 discloses an injection device for administering a medicament to a subject, the device being powered by a pyrotechnic charge. WO 01/89612 discloses an injection device powered by an internal combustion engine.
In particular, WO 01/89612 teaches that the fuel/air mixture burnt in the combustion chamber should preferably be compressed prior to combustion. The document discloses in detail one way of effecting such compression, which relies on the user manually to depress a plunger. The document also states that the process “may be effected automatically” but does not disclose any embodiment where compression of the fuel/air mixture is achieved automatically and it is not immediately apparent how this could be done.
The present invention aims to provide a portable device powered by an internal combustion engine in which a fuel/combustion-supporting gas mixture is compressed to a pressure in excess of the ambient atmospheric pressure, and wherein operation of the device is at least partly automated.